Adequate nutrient intake should be provided for the cure of children diagnosed with cancer. The aim of this study was to evaluate serum trace elements and vitamins of children with cancer at diagnosis and during treatment. Children with newly diagnosed cancer who were admitted to our center were evaluated for serum selenium, iron, ferritin, C-reactive protein, vitamin B12, folate, and 25-OH vitamin D levels at presentation, and at the third and sixth months of cancer treatment. Forty-two children (male/female: 15/27) with a median age of 8 years (range, 2 to 17) were included in the study. Mean serum B12, folate, and iron levels were within normal ranges, but selenium and 25-OH vitamin D were low at presentation and during the 6-month period. Serum ferritin levels were high in all 3 measures, but they decreased significantly at the sixth month (P=0.04). There was no relation between micronutrient deficiency and sex, or primary disease, or stage, or place of residence of the patient. In conclusion, serum trace element and vitamin deficiencies are common in children with cancer, and there is a need for further studies with larger patient series.